Assuming you're using preferences that is scoped to a user (i.e., owner type is user) then the behavior you're describing is correct. When user1, user2, and admin changes the preference, they're only changing it for himself. To achieve what you want, you'll need to do some customization since different users will have different expectation on this. You want the admin's changes to override, but others might want the admin's values to be defaults.
